fix(docs): add sidebar ordering for Design Thinking documentation

[WilliamBerryiii]

The Design Thinking documentation section lacked sidebar ordering metadata, causing pages to render in alphabetical order rather than a logical learning sequence. This PR added sidebar_position frontmatter to all 16 Design Thinking pages, created a category.json for the section, and adjusted downstream category positions to maintain a coherent sidebar hierarchy.

Design Thinking was placed at position 5 in the sidebar, after Getting Started, HVE Guide, and RPI. This positions it after the foundational "what is this?" and "core daily workflow" sections, recognizing that DT is a methodology users explore once they understand the platform basics.

Changes

• Created category.json for the Design Thinking section at sidebar position 5, with collapsible navigation and a generated index page
• Added sidebar_position frontmatter to all 16 Design Thinking markdown files, ordered as a learning progression: overview (README.md), methodology (why-design-thinking.md), tools (dt-coach.md, dt-learning-tutor.md), methods 1-9 in sequence, then integration guides
• Bumped sidebar positions for 5 downstream categories (Agents, Architecture, Contributing, Security, Templates) by +1 to accommodate the new Design Thinking entry
• Updated the category hierarchy list in .github/instructions/docusaurus-edits.instructions.md to reflect the revised ordering

Related Issues

Closes #830

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None